1. Field of the Invention
The invention relates to a method in an ebullated bed process for changing feedstock from a sediment yielding feedstock to a different sediment yielding feedstock.
2. Description of Other Relevant Methods in the Field
The ebullated bed process comprises the passing of concurrently flowing streams of liquids, or slurries of liquids and solids, and gas through a vertically cylindrical vessel containing catalyst. The catalyst is placed in random motion in the liquid and has a gross volume dispersed through the liquid greater than the volume of the mass when stationary. The ebullated bed process has found commercial application in the upgrading of heavy liquid hydrocarbons and converting coal to synthetic oils.
The process is generally described in U.S. Pat. Re No. 25,770 to Johanson incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas pass upwardly through the bed. The catalyst bed motion is controlled by a recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapors along with the liquid which is being hydrogenated pass through that upper level of catalyst particles into a substantially catalyst free zone and are removed from the upper portion of the reactor.
Reactors employed in a catalytic hydrogenation process with an ebullated bed of catalyst particles are designed with a central vertical recycle conduit which serves as the downcomer for recycling liquid from the catalyst free zone above the ebullated catalyst bed to the suction of a recycle pump to recirculate the liquid through the catalytic reaction zone. The recycling of liquid from the upper portion of the reactor serves to ebullate the catalyst bed, maintain temperature uniformity through the reactor and stabilize the catalyst bed.
U.S. Pat. No. 4,053,390 to L. C. James teaches a start-up procedure for an ebullated bed process. In the procedure, a light oil is used to establish an ebullating bed. A heavy residual oil feedstock is incrementally substituted for the light oil. Hydrogen gas flow rate and ebullating pump speed are set to maintain ebullated bed expansion. In the incrementally changing feed stream, viscosity is controlled within .+-.10% and specific gravity controlled within .+-.5% to maintain a constant expansion of the ebullated bed, at a constant ebullating pump rate and gas flow rate.
U.S. Pat. No. 3,809,644 to A. R. Johnson et al. teaches a multiple stage ebullated bed hydrodesulfurization process. In the process catalyst is poisoned by the deposition of 100 to 700 ppm metals, principally nickel and vanadium from the vacuum resid feedstock. In the process used catalyst is passed sequentially from down stream reactors to upstream reactors thereby extending the economic life of the catalyst.